It's a question of what YOUR standard of "clean" is
When I take enemas, I almost always do "enemas till clear" which means one enema at least, stays in for 15 minutes or something close to that and comes out "clear"
Yellow without any food scraps IS a "clear return"
Every body is different, and you should listen to yours.
For me, that's typically 3-4 rounds of my standard enema. More if I didn't start with an empty stomach.
Understand that the stomach releases part of it's contents to the small intestine about every 15 minutes, give or take about 3 minutes.
Likewise the small intestine releases part of it's content into the large intestine at the same rate, but almost never in sync.
If the stomach is empty the small intestine slows the time and reduces the amount released to the large intestine.
A good round of 2-4 enemas should clear out the large intestine, and going 8 hours without solid food should effectively empty the stomach, at minimal risk. UNDER NO CIRCUMSTANCES SHOULD YOU FORCE YOURSELF TO VOMIT!! That is simply too dangerous! There IS NO safe way!
If you want to do a more thorough cleanse that involves emptying the small intestine as well, that takes a different approach with at least some laxatives, in addition to the enemas.
If at any time during the enemas you ever feel more than mild nausea, or any dizziness or light-headedness it's time to at a minimum WAIT longer between rounds, consider pulling the plug for at least a number of days.
If you don't go at least several days of normal movements without ANY enemas, laxatives, suppositories etc. you are overdoing it!!!